Analysis of microplastic flux from the Gediz River to the Aegean Sea: A modeling study for environmental management

It is critical to determine the abundance of microplastics in terrestrial inland waters, understand their fate and transport mechanisms, and reveal their status in aquatic environments. This study aimed to develop and calibrate a mathematical model to simulate microplastic (MP) pollution in the Gediz River Basin, Türkiye, which focused on MP fate and transport under existing conditions and various management scenarios. The baseline scenario revealed that, despite a ninefold difference in flow rates, the midstream and upstream parts of the basin also exhibited significant contamination, with an average concentration of 25 n/L compared to the downstream average of 29 n/L. The model was later simulated to test the effects of various mitigation scenarios including but not limited to reducing MP discharges from wastewater treatment plants (WWTPs) and implementing vegetative barriers in tributaries. Scenario 4, which involves reducing MP concentrations in upstream tributaries with vegetative barriers, achieved the highest average reduction across all segments (32 %) and specifically in the downstream area (47 %). In contrast, Scenario 1, aimed at reducing wastewater discharges from urban and industrial WWTPs through water reclamation, and Scenario 2, which focused on eliminating MP in Organized Industrial Zone (OIZ) discharges by changing industrial inputs, achieved the most effective MP reductions in the upper basin, with reductions of 20 % and 17 %, respectively. Scenario 3, targeting flow reduction and accumulation through constructed wetlands, had minimal impact, with reductions close to 0 % in most areas. These results highlight the need for comprehensive approaches to effectively reduce MP pollution, particularly in managing upstream and tributary sources.